Heather yarns are produced by cospinning differently dyed or dyeable filaments to provide different colors or shades in a given multifilament yarn. Spinning apparatus for such cospinning is designed to provide a given flow rate of each of the two (or more) fiber-forming spinning solutions or melts. It is often desirable to change the weight ratio of component filaments in the resultant yarn so as to provide products with a range of heather effects. With a given spinning machine, any such change from design capacities lowers the productivity of the machine. To change the machine design each time a weight-ratio change in the product is desired is prohibitively expensive.
The art needs ways and means to feed to a given spinning machine a constant flow rate of two spinning solutions and, at the same time, to adjust the spinning conditions so as to provide an apparent change in the weight ratio of these two spinning solutions in the final yarn when in fact no change has been made in the flow rate of either component.